As silicones having a hydrophilic group, a variety of modified silicone compounds are known, and among nonionic systems, polyether-modified silicones have been widely used since the past. Additionally, (poly)glycerin-modified silicones (Patent Documents 1 to 9) and sugar- and polysaccharide-modified silicone compounds (Patent Document 10) have also been reported. Low-HLB polyether-modified silicones are outstanding emulsifiers capable of providing W/O emulsions with excellent stability while having fluidity with low viscosity, and therefore have been widely used particularly in the field of cosmetic products.
In contrast, silicones modified with polyglycerins, sugars, or polysaccharides have the problems that the degree of freedom in structural design is low and they do not have a wide range of use. These polyhydric alcohol-modified silicones are normally produced by adding a polyhydric alcohol derivative containing a reactive unsaturated group to an organohydrogensiloxane, but in many cases, miscibility of residual polyhydric alcohol derivative and the polyhydric alcohol-modified silicone that is the reaction product is low, and the appearance is cloudy and non-uniform, and phase separation occurs within a short time after production.
Additionally, because miscibility of organohydrogenpolysiloxanes and polyhydric alcohol derivatives is inherently low, if the molecular weight of a polyhydric alcohol-modified silicone exceeds roughly 5000, there has been the problem that the addition reaction does not come to completion even if a solvent is used, and production of the targeted product is often difficult. Furthermore, even when the molecular weight is approximately 3000, there has been a problem from the viewpoint of production efficiency as well, in that unreacted matter gradually separates and settles and an operation to remove it is required.
Furthermore, even if a compound in which the hydroxyl group is protected is used as the polyhydric alcohol derivative, the problem of separation described above is unavoidable because deprotection is necessary after the reaction ends. Also, with this method, acid treatment conditions for deprotection are inevitably harsh and breakage of the silicone backbone occurs, and as a result, there is the problem that the desired product cannot be obtained with good reproducibility.
Patent Document 7 proposes a method for producing a branched polyglycerol-modified silicone obtained by adding/graft polymerizing a silicone having at least one functional group selected from the group consisting of hydroxy groups, carboxy groups, amino groups, imino groups, mercapto groups, and epoxy groups, with 2,3-epoxy-1-propanol in the presence of an acidic or basic catalyst. With this method, however, the siloxane backbone breaks during graft polymerization, and as a result, two or more components having different properties tend to be produced as copolymers, and there are many problems from the perspectives of quality and the purification process.
In response to these problems, it has been attempted to improve transparency of polyhydric alcohol-modified silicone compositions that are reaction products by reducing the amount of residual polyhydric alcohol derivative, which causes cloudiness and phase separation, by repeating microfiltration and adsorbent treatment. However, these impurities are ordinarily liquids in the temperature range in which the polyhydric alcohol-modified silicone that is the main component is in the liquid phase, and therefore a technique of solid/liquid separation utilizing a filter aid, a cartridge filter, or the like is not only irrational, but is also mostly ineffective in actuality. For this reason, after the majority of the impurities are first extracted out in a highly hydrophilic solvent, an operation of further removing residual liquid impurities from the polyhydric alcohol-modified silicone that is the main component by a filtration process using an adsorbent such as activated carbon is required (or, conversely, the main component is extracted in a hydrophilic solvent). Incidentally, phase separation in the extraction process ordinarily takes time, and this does not yield clean separation. This results in an increase in waste and a decrease in yield and productivity. Furthermore, in many cases the system as a whole goes into an emulsified state and separation is impossible due to the structure of polyhydric alcohol-modified silicone, and since it cannot be generally used from the perspective of industrial production, this problem is still not resolved at present.
Recently, Patent Document 8 has proposed a novel alternating copolymer of organopolysiloxane with polyglycerine derivative, and suggests that a high molecular weight polyglycerine-modified silicone can be obtained without the problem of white turbidness, and the like, caused by the unreacted starting material occurring. However, it is clear from the chemical structure that this compound has a hydrophilic group portion incorporated on its backbone. As a result, this copolymer has properties completely different that those of conventional general-use hydrophilic silicones such as polyether-modified silicone and the like and, therefore, a high level of technical skill is necessary to stably compound this copolymer in delicate formulations such as cosmetic products and the like, leading to the problem of the field of use being limited.
For the reasons described above, the current situation is that conventional polyhydric alcohol-modified silicones have little practical utility and inevitably lack variation in chemical structure. Therefore, there has been a demand for the development of a stable polyhydric alcohol-modified silicone that is easy to produce and incurs almost no phase separation or sedimentation of unreacted starting material or the like after production, and a method for producing the same.
Thus, in Patent Document 11, the present inventors disclose a novel organopolysiloxane containing a hydrophilic group, which is easy to produce and incurs almost no phase separation or sedimentation of unreacted starting material and the like after production, and is chemically stable and has excellent practicality, and a method for producing the same. In particular, they propose that this organopolysiloxane be used as a surfactant, powder treatment agent, and surface treatment agent that can be advantageously used in the field of cosmetics.
The novel organopolysiloxanes containing a hydrophilic group produced by the technique disclosed in Patent Document 11 are uniform and stable compositions, but since many of them appear cloudy or translucent, they sometimes have the problem that they simply look unattractive, depending on the user. Additionally, from the presumption that an opaque appearance implies low miscibility between the main component and impurities, there have been also users who have concerns about the possibility of potential phase separation after the quality guarantee period of the product elapsed even if there is no problem within that period. In these respects, there has been still room for improvement in the novel organopolysiloxanes containing a hydrophilic group proposed in the past by the present applicants (Patent Document 11).